The present invention relates to an exhaust cleaning device of a diesel engine able to precisely judge a regenerating period of a filter for catching and collecting a particulate matter within exhaust gas.
The disclosure of Japanese Patent Application No. 2006-106674 filed on Apr. 7, 2006 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
In the diesel engine, the particulate matter (PM) included within the exhaust gas is conventionally caught and collected by a filter (DPF: Diesel Particulate Filter) interposed in an exhaust passage. In DPF, the flowed-in exhaust gas passes a porous partition wall and PM is caught and collected by a surface of the partition wall and a fine hole.
PM caught and collected in DPF is deposited with the passage of time. Therefore, after PM reaches a predetermined amount, regeneration processing for removing PM is performed for the purpose of prevention of clogging. Post injection for performing after-injection of fuel and supplying the fuel before DPF is known as a technique for removing PM deposited in DPF. Exhaust gas temperature is raised by the post injection and PM is oxidized and removed.
The DPF regeneration is started when a generating amount of PM is presumed at any time from an engine operating state and an integrating PM amount calculated by integrating this generating amount reaches a set amount. Otherwise, the DPF regeneration is started when a state (exhaust temperature, exhaust pressure, etc.) within the exhaust passage is monitored and it is judged that DPF is clogged.
It is difficult to univocally presume the integrating PM amount on the basis of the operating state of the engine since there is dispersion in the engine. Accordingly, it is difficult to precisely judge the DPF regenerating period. Therefore, when the DPF regeneration is started on the basis of the integrating PM amount, it is required that a threshold value for examining whether the integrating PM amount reaches a predetermined integrating amount or not is set to a safe direction, i.e., is lowly set. However, when the threshold value is lowly set, a DPF regeneration time number is increased and a post injection time number is correspondingly increased. Therefore, a problem exists in that fuel cost becomes worse.
On the other hand, when DPF is judged from the state within the exhaust passage, it is difficult to clearly distinguish a state causing no clogging and a state generating the clogging. In reality, no clogging can be judged when it exceeds no limit of the PM integrating amount desirous to be regenerated. When the regeneration processing after it exceeds the limit of the PM integrating amount is repeatedly performed, a problem exists in that deterioration of DPF is promoted and a reduction of durability is caused.
To cope with this problem, for example, patent literature 1 (JP-A-2003-155916) discloses a technique for measuring a differential pressure before and after DPF and examining whether the clogging is generated or not while the presumed integrating PM amount exceeds no threshold value set in advance.
In the technique disclosed in this literature, when it is judged that DPF is clogged from the differential pressure before and after DPF, manual execution of compulsory regeneration using the operation of a regeneration button of a driver's seat is urged, and DPF is compulsorily regenerated.
[Patent literature 1] JP-A-2003-155916
As mentioned above, there is dispersion in the engine. In the technique disclosed in patent literature 1, the threshold value for examining whether the integrating PM amount reaches an integrating amount set in advance or not is a fixed value. Therefore, this dispersion of the engine cannot be absorbed, and it is difficult to precisely judge the DPF regeneration period.
Further, when the clogging is detected from the differential pressure before and after DPF, the manual execution of the DPF regeneration is merely urged. Therefore, the DPF regeneration period is easily missed. When the DPF regeneration period is repeatedly missed, deterioration of DPF is promoted and a reduction of durability is caused.